1. Field of the Invention
The present invention generally relates to a light emitting diode (LED) and a method thereof. More particularly, the present invention relates to a LED structure having electrostatic discharge (ESD) protection function.
2. Description of Related Art
In general, light emitted by a light emitting diode (LED) comprising a III–V compound semiconductor material has a wide bandgap of emitting light covering almost all the wavelength range of infrared (IR), ultra-violet (UV) and visible light. For a LED device, the internal quantum efficiency and the external quantum efficiency (or so-called light extraction efficiency) are two important parameters. Conventionally, the method of increasing the internal quantum efficiency is to improve the crystal quality of the light emitting layer and the design of the layer structure. The method of increasing the external quantum efficiency is to reduce energy loss of the light emitted by the light emitting layer by reducing total reflection or other effect in the LED device.
Since the luminous efficiency of LED has been enhanced drastically, conventional fluorescent lamp and incandescent bulb are gradually replaced by LED and applied in many applications. For example, LED may be provided as a light source for a variety of electronic appliances, such as, scanner that requires high response speed, a liquid crystal display (LCD), a driving panel of a motor, traffic light, and other conventional lighting devices. Furthermore, the advantages of LED in comparison with conventional bulb are, for example, small size, long lifetime, low driving voltage/current, non-fragile, low thermal generating in operation, low contamination (mercury free), low power consumption and high luminous efficiency. It is noted that, although LED has so many advantages described above, however, the disadvantages of the LED is that it gets easily damaged by an abnormal voltage or electrostatic discharge (ESD). Therefore, a conventional method for preventing the damage is to connect a Zener diode in parallel to the LED from the abnormal voltage or electrostatic discharge.
FIG. 1 is an equivalent circuit diagram schematically illustrating a LED package structure having a conventional electrostatic discharge (ESD) protection circuit. Referring to FIG. 1A, to avoid the damage of LED 30 from the electrostatic discharge during operation, the LED 30 and a Zener diode 40 are connected in parallel. The Zener diode 40 is operated in the breakdown region, thus the Zener diode 40 remains electrically conducted. Therefore, when a normal forward voltage is applied to the two ends V+ and V− of LED 30, the LED 30 is operated normally. However, when an abnormal voltage or electrostatic charge is generated, the over level high voltage is discharged by the Zener diode 40 that operates in the breakdown region. Therefore, the LED 30 is protected from the damage of the abnormal voltage or high voltage due to the abnormal electrostatic charge, and an irreversible damage to the LED 30 can be avoided.
FIG. 1B is a cross-sectional view schematically illustrating a LED package structure having a conventional electrostatic discharge (ESD) protection circuit. Referring to FIG. 1B, the gallium nitride (GaN) LED 30 of FIG. 1 includes a transparent substrate 32, a N-type a doped gallium nitride (GaN) layer 34, a P-type doped gallium nitride (GaN) layer 36 and two electrodes 38a, 38b. The Zener diode 40 of FIG. 1A comprises an N-type doped silicon 42, a P-type doped silicon 44 and metal layers 46a, 46b. Furthermore, the bumps 50a, 50b of FIG. 1B is generally composed of a solder material. The P-type doped silicon 44 is electrically connected to the N-type doped gallium nitride (GaN) layer 34 by the bump 50a, and the N-type doped silicon 42 is electrically connected to the P-type doped gallium nitride (GaN) layer 36 by bump 50b. 
In summary, although the circuit structure described above can prevent the LED from the damage due to the electrostatic discharge. However, the process of fabricating the circuit structure is complicated as it requires a number of additional process steps, such as, the step of forming the P-type doped silicon 44 in the N-type doped silicon 42 requiring expensive apparatus, namely, an ion implanter, related gas supporting devices and vacuum system. Accordingly, the overall packaging time and cost of the LED structure having conventional electrostatic discharge (ESD) protection circuit are increased.